YA books

Adult books that could double for YA:
The Glass Castle, by Jeannette Walls
The Handmaid's Tale, by Margaret Atwood (also Cat's Eye, Oryx and Crake, and The Blind Assassin)
The Edible Woman, by Margaret Atwood
The Virgin Suicides, by Jeffrey Eugenides

Chick Lit (a working definition of the term):
Rules of the Road, by Joan Bauer
The Disreputable History of Frankie Landau-Banks by E. Lockhart
I Capture the Castle, by Dodie Smith
The Austins books, by Madeline L'Engle
The Young Unicorns, by Madeline L'Engle
A House Like a Lotus, by Madeline L'Engle
The Small Rain and A Severed Wasp, by Madeline L'Engle
The Pistachio Prescription, by Paula Danziger
The Cat Ate My Gymsuit, by Paula Danziger
This Place Has no Atmosphere, by Paula Danziger
The Anastasia books, by Lois Lowry 

Not quite chick lit, but with heroines:
The Tillerman Cycle books, by Cynthia Voight (Homecoming, Dicey's Song, etc.)

Contemporary YA with male main characters:
Godless, by Pete Hautman
Marcelo in the Real World, by Fransisco X Stork
The Curious Incident of the Dog in the Night-Time, by Mark Haddon
Slam, by Nick Hornby 
Rule of the Bone, by Russell Banks 
Where Things Come Back, by John Corey Whaley

Dystopian future books:
Feed, by M.T. Anderson
The Hunger Games, by Suzanne Collins
The Handmaid's Tale, by Margaret Atwood
Ship Breaker, by Paolo Bacigalupi
Divergent and Insurgent, by Veronica Roth

Edgy issues:
Rule of the Bone, by Russell Banks
The Edible Woman, by Margaret Atwood
Wintergirls, by Laurie Hals Anderson
Thirteen Reasons Why, by Jay Asher
The Fault in Our Stars, by John Green
Eleanor & Park, by Rainbow Rowell

Fantasy/Sci Fi:
Graceling, by Kristin Cashore
Bitterblue, by Kristin Cashore
The Knife of Never Letting Go, by Patrick Ness (Chaos Walking trilogy)
The Hunger Games trilogy, by Suzanne Collins
His Dark Materials (The Golden Compass and sequels), by Philip Pullman
the Avatars series, by Tui T. Sutherland
Across the Universe, by Beth Revis
The Wrinkle in Time trilogy, by Madeline L'Engle
Jackaroo, by Cynthia Voight
The Lord of the Rings, by J.R.R. Tolkien 
Ender's Game, by Orson Scott Card
Dark Lord of Derkholm, by Diana Wynne Jones
Philip Pullman's His Dark Materials Trilogy (the Golden Compass books)
The Percy Jackson series, by Rick Riordan (also here and here)
Mortal Instruments, by Cassandra Clare
Flowers for Algernon, by Daniel Keyes (though I'd call it more "speculative fiction")
Goblin Secrets, by William Alexander
Divergent and Insurgent, by Veronica Roth
A Corner of White, by Jaclyn Moriarty
The Last Apprentice, by Joseph Delaney
the Leviathan trilogy, by Scott Westerfeld
the I, Q series, by Roland Smith

Gay and Gay-friendly YA:
A House Like a Lotus, by Madeline L'Engle
Annie on My Mind, by Nancy Garden
Skim, by Mariko Tamaki
Awkward, Definition, Potential, and Likewise, by Ariel Shrag
Keeping You a Secret, by Julie Anne Peters
and many more...
Will Grayson, Will Grayson, by David Levithan and John Green
Geography Club, by Brent Hartinger
Am I Blue?: Coming Out from the Silence (anthology) ed. Marion Dane Bauer
The Weetzie Bat books, by Francesca Lia Block
Girl Goddess #9, by Francesca Lia Block

Graduation gifts:
100 Words Every High School Freshman Should Know
100 Words Every High School Graduate Should Know

Graphic novels:
American Born Chinese, by Gene Luen Yang
In the Shadow of No Towers, by Art Spiegelman (quite an adult book)
Persepolis, by Marjane Satrapi
Skim, by Mariko Tamaki
Awkward, Definition, Potential, and Likewise, by Ariel Shrag
Ian Pollock's Illustrated King Lear
Othello

Historical fiction:
Kindred, by Octavia Butler
the Sally Lockhart mysteries, by Philip Pullman
The Eagle of the Ninth, by Rosemary Sutcliff 
The Agency series, by Y.S. Lee
Code Name Verity, by Elizabeth Wein

Humor:
The Secret Diary of Adrian Mole, Age 13 3/4, by Sue Townsend
The Hitchhiker's Guide to the Galaxy, by Douglas Adams
Dark Lord of Derkholm, by Diana Wynne Jones

Male equivalent of chick lit:
The Eagle of the Ninth, by Rosemary Sutcliff 
The Lord of the Rings, by J.R.R. Tolkien
Ender's Game, by Orson Scott Card 
The Secret Diary of Adrian Mole, Age 13 3/4, by Sue Townsend
Rule of the Bone, by Russell Banks  

Mystery:
The Young Unicorns, by Madeline L'Engle
The Westing Game, by Ellen Raskin
Brat Farrar, by Josephine Tey
The Man in the Brown Suit, by Agatha Christie
The Tommy and Tuppence mysteries, by Agatha Christie
the Sally Lockhart mysteries, by Philip Pullman
The Agency series, by Y.S. Lee

Nonfiction:
The Fairy Ring, by Mary Losure

Poetry (adult, but great for YA readers):
archy and mehitabel, by Don Marquis 
Spoken word poets Alvin Lau, Sarah Kay, and Andrea Gibson
Mary Oliver, e.e. cummings, Lucille Clifton, Billy Collins, Sarah Teasdale, Frank O'Hara and more

Plays:
with their eyes, ed. Annie Thoms

Time travel:
Kindred, by Octavia Butler

Why we don't like Twilight.

Books for teens who like Twilight:
A Great and Terrible Beauty, by Libba Bray (the Gemma Doyle trilogy)

War:
Doonesbury, by Garry Trudeau
The Things They Carried, by Tim O'Brien